The present invention relates to a seat belt retractor having a load limiter.
U.S. Pat. No. 6,290,159 B1 teaches a seat belt retractor with a load limiter having a flowable medium which is transported, by a displacement device, such as a hydraulic pump, driven by the belt webbing unwound from the belt reel, at an energy consumption related to a crash and adjusted as a function of data related to a crash. For this purpose, the cross-section of flow of the displaced or transported fluid may be adjusted by a controllable valve.
In the present invention the flow resistance of the medium transported by the displacement device is adjusted. This adjustment is preferably performed as a function of the seat position and the body weight of the vehicle occupant wearing the seat belt and affected by a crash, and by the severity of the crash. Furthermore, during the force-limiting withdrawal of the belt webbing, it is possible for a constant or characteristic-controlled belt webbing restraining force to be obtained by adjusting the flow resistance.
The flow rate of the transported medium can be adjusted and thus the desired restraining force coming from the belt webbing obtained. The corresponding flow resistance and thus the desired flow of the transported load-limiter medium through the hydraulic system of the load limiter may be achieved by a number of embodiments.
For example, a valve wherein the timing is controlled by an electronic control device and which, as a function of the input parameters relating to a crash, adjusts the through flow quantity of the transported load-limiter medium per unit time may be provided. This is achieved by the timing of opening and closing of the valve.
Furthermore, the transported medium may be countered by a counter-force that acts over the entire cross-section of the transported load-limiter medium. This counter-force counters the pressure of the transported force-limiter medium and may, for example, be in an adjustable pneumatic spring or a mechanical spring of variable spring force. As a result of this counter-force or counter-pressure, it is also possible to adjust the restraining force coming from the fastened seat belt webbing.
Furthermore, the mass flow of the transported load-limiter medium may be used as a regulating variable for the restraining force or withdrawal speed exerted by the belt webbing. In the case of a system responsive to mass flow of this kind, an element which is mounted in the flow path in opposition to a restoring force, for example a spring force, and around which the load-limiter medium flows may be provided. This element around which there is flow is moved in opposition to the restoring force by the mass flow of the transported medium, and in so doing adjusts the cross-section of flow as a function of the mass flow.
Furthermore, by altering the viscosity of the load-limiter medium the load-limiting action may be adjusted. Suitable load-limiter media are preferably electro-rheological and/or magneto-rheological fluids wherein the viscosity may be adjusted by an electrical and/or magnetic field. The displacement device may be constructed such that it transports the load-limiter medium in the manner of a hydraulic pump. Alternatively the displacement device is moved in the load-limiter medium at rest by the force exerted by the belt webbing, in which case the load-limiter medium is transported by the displacement device. The displacement device may be a rotor or a linearly movable piston.
As a result of the present invention, the space which is available for the forward displacement of the vehicle occupant wearing the seat belt is exploited for force-limited forward displacement. In the case of a vehicle occupant of high weight, therefore, the restraining force is greater than for a vehicle occupant of lower weight. In the present invention, this is achieved by an appropriate adjustment of the flow rate or the flow resistance through electronic or electrical or automatic regulation.